1. Field of the Invention
This invention relates to an aqueous silicone emulsion which gives a silicone elastomer upon removal of the water under ambient conditions.
2. Background Information
A silicone rubber latex reinforced with silsesquioxane is taught in U.S. Pat. No. 3,355,406, issued Nov. 28, 1967, by Cekada. He teaches a latex containing a curable, essentially linear silicone polymer, preferably a hydroxy or alkoxy endblocked linear polymer having been prepared by emulsion polymerization, a crosslinking agent which is a trifunctional or tetrafunctional silane, preferably trialkoxysilane, and a catalyst. Included in the catalysts are dialkyltindiacylates.
Ichikawa, et al. describe silicone compositions which are useful as binders for fibrous gasketing and packing materials in U.S. Pat. No. 4,100,124, issued Jul. 11, 1978. The compositions are a mixture of hydroxyl end-blocked diorganosiloxanes, a crosslinking trialkoxysilane, catalyst, emulsifier, and water.
Johnson et al. describe in U.S. Pat. No. 4,221,688, issued Sep. 9, 1980, a silicone emulsion which provides an elastomeric product and methods for its preparation. The emulsion comprises a continuous aqueous phase and a dispersed phase, the dispersed phase consisting essentially of an anionically stabilized hydroxylated polydiorganosiloxane which contains about 2 silicon-bonded hydroxyls per molecule, an organic tin compound, and a colloidal silica, the emulsion having a pH in the range of 9 to 11.5 inclusive. Experience with such emulsions has now shown that there is a problem with the shelf life of the emulsion, which is manifested by a change in properties of the elastomer obtained upon drying as the emulsion ages; and, in addition, a change in properties upon aging of the elastomer produced by the removal of water from the emulsion.
A silicone elastomeric emulsion having improved shelf life is taught by Elias and Freiberg in U.S. Pat. No. 4,427,811, issued Jan. 24, 1984. The emulsion is produced by a method which first mixes an anionically stabilized, hydroxyl endblocked polydiorganosiloxane, colloidal silica, and an alkyl tin salt, then ages the mixture for at least two weeks at room temperature, then adds filler other than colloidal silica. The alkyl tin salt is preferably a dialkyltindicarboxylate.
A different type of aqueous emulsion is taught in U.S. Pat. No. 4,618,642, issued Oct. 21, 1986, by Schoenherr. This composition consists essentially of an anionically stabilized, hydroxyl endblocked polydiorganosiloxane, a dialkyltindicarboxylate, a trifunctional silane crosslinking agent, and a non-siliceous, inert filler. The filler is non-siliceous since the shelf life will be affected if a silica filler is present because the composition still contains the hydroxylated polydiorganosiloxane and organic tin compound as found in Johnson et al.